1. Field of the Invention
This invention relates to a method for forming rings such as plow rings on pile shells, by bending lengths of material cut from continuous elongated stock, and to apparatus for carrying out the method.
2. Brief Description of the Prior Art
The present invention is particularly directed to the manufacture of plow rings for pile shells. These plow rings are attached to the lower end of thin tubular pile shells to be engaged by a driving mandrel used to drive the shell into the earth before it is filled with concrete. These plow rings are formed by bending lengths of heavy stock of irregular cross sectional shape and this presents a problem of forming the stock into rings.
It is known to form plow rings by cutting long lengths of stock such as bar, strip or wire material into smaller lengths and then bending the smaller lengths around cylindrical mandrels. However, because of the thickness of the stock and its irregular cross sectional shape it tends to spring back from the mandrel and this makes it difficult to form the rings.
It has been proposed to automate the above described ring forming operations by means apparatus employing a number of mandrels, each mandrel adapted to a different stage in the cutting and bending process. U.S. Pat. No. 4,132,106, for example suggests to use a first partially circular rotatable mandrel in connection with a first bending roller that moves around the mandrel to apply a partial circular bend to a length of stock, as a first clamp secures the stock against movement during the bending. A punch then cuts the stock in the middle of the bend while a second clamp secures the opposite end of the cut length, which had been partially bent in a previous operation cycle, against a second mandrel. A second forming roller is then positioned against the second mandrel which is thereafter rotated to complete the bending operation, and the completed ring is removed. The now pre-bent end of the stock is advanced by an amount corresponding to the circumference of the ring and the operation is repeated.
U.S. Pat. No. 3,580,030 proposes a somewhat similar technique but using a first mandrel for curving both ends of each cut length of stock and a second mandrel for subsequently curving the center portion.
The known prior art does not solve the problem of forming rings accurately and in a continuous and economical manner.